This invention relates to methods and apparatus for fusing coil leads to electric motor armature commutators. More particularly, the invention relates to methods and apparatus for ensuring that commutators are well balanced after coil leads are formed.
Machines for fusing coil leads to the commutators of electric motor armatures are well-known. Fusing machines are used to attach the leads to the commutators after the coils have been wound onto the armatures. Good electrical contacts and strong mechanical bonds between the leads and the commutators are formed by using a combination of heat and pressure. For example, commonly-assigned U.S. Pat. No. 5,063,279, which is hereby incorporated by reference herein, and commonly-assigned U.S. Pat. No. 5,300,753 which is hereby incorporated by reference herein, describe fusing machines which have electrodes that are used to compress deformable tangs onto leads while simultaneously supplying an electric current. As the current passes through a tang, the adjacent area is heated, which vaporizes a portion of the electrical insulation on the lead. By vaporizing the insulation, a clean electrical contact is formed between the lead and the commutator. Each tang is also compressed firmly enough to form a strong mechanical bond.
Electric motor armatures typically contain imperfections, such as slight variations in the diameter of the commutator, which can adversely affect armature balance. Unbalanced armatures cause motor vibration and excessive motor wear. Typically, the primary concern when forming fused connections has been to avoid either compressing a tang insufficiently, which can lead to a weak connection, or compressing a tang too much, which can sever the lead. As a result, fusing machines generally monitor the relative displacement between the electrode used to form the lead connection and the commutator bar that contains the tang, so that tangs are compressed to an equal degree.
However, if there are substantial variations in the radial positions of the commutator bars due to imperfections in the armature, the conventional approach, in which all tangs are compressed equally during fusing, leaves the commutator, and therefore the armature, unbalanced. It would therefore be desirable to balance the armature commutator by compressing some tangs to a greater extent than others during the fusing operation.